Techniques (pattern-forming techniques) in which a fine pattern is formed on top of a substrate, and a lower layer beneath that pattern is then fabricated by conducting etching with this pattern as a mask are widely used in the production of semiconductor devices and liquid display device. These types of fine patterns are usually formed from an organic material, and are formed using a lithography method or a nanoimprint method or the like. For example, in a lithography method, a resist film is formed on a support such as a substrate using a resist material containing a base component such as a resin; the resist film is selectively exposed to a radial ray such as light, electron beam or the like; and developing treatment is conducted to form a resist pattern having a predetermined shape on the resist film. Further, using the resist pattern as a mask, the substrate is processed by etching, so as to produce a semiconductor or the like.
The resist material is classified into a positive-type and a negative-type. A resist material in which the exposed portions exhibits increased solubility in a developing solution is called a positive-type. On the other hand, a resist material in which the exposed portions exhibit decreased solubility in a developing solution is called a negative-type.
In general, an aqueous alkali solution (alkali developing solution) such as an aqueous solution of tetramethylammonium hydroxide (TMAH) is used as the developing solution. Alternatively, an organic solvent such as an aromatic solvent, an aliphatic hydrocarbon solvent, an ether solvent, a ketone solvent, an ester solvent, an amide solvent or an alcohol solvent is used as the developing solution.
Advances in lithography techniques have led to progress in the field of pattern miniaturization.
Typically, these miniaturization techniques involve shortening the wavelength (increasing the energy) of the exposure light source. Conventionally, ultraviolet radiation typified by g-line and i-line radiation has been used, but nowadays KrF excimer lasers and ArF excimer lasers are starting to be introduced in mass production. Furthermore, research is also being conducted into lithography techniques that use an exposure light source having a wavelength shorter (energy higher) than these excimer lasers, such as electron beam (EB), extreme ultraviolet radiation (EUV), and X ray.
As the wavelength of the exposure source becomes shorter, resist materials are required to have lithography properties such as a high resolution capable of reproducing patterns of minute dimensions, and a high level of sensitivity to these types of exposure light sources. As resist materials which satisfy such requirements, chemically amplified resists are known.
As a chemically amplified composition, a composition including a base material component that exhibits a changed solubility in a developing solution under the action of acid and an acid-generator component that generates acid upon exposure is generally used. For example, in the case where an alkali developing solution is used as a developing solution (alkali developing process), a base component which exhibits increased solubility in an alkali developing solution under action of acid is used.
Conventionally, a resin (base resin) is typically used as the base component of a chemically amplified resist composition. Currently, resins that contain structural units derived from (meth)acrylate esters within the main chain (acrylic resins) are now widely used as base resins for chemically amplified resist compositions that use ArF excimer laser lithography, as they exhibit excellent transparency in the vicinity of 193 nm
In general, the base resin for a chemically amplified resist composition contains a plurality of kinds of structural units for improving lithography properties and the like. When the base resin is an acrylic resin, as the acid decomposable group, in general, resins in which the carboxy group of (meth)acrylic acid or the like is protected with an acid dissociable group such as a tertiary alkyl group or an acetal group are used.
For example, referring to Patent Literature 1, it is disclosed that an alkali-insoluble or alkali-hardly-soluble polymer containing 2 or more structural units including a structural unit containing a specific acid decomposable group is used in improving properties useful for minute processing.
Further, referring to Patent Literature 2, it is disclosed that the solubility of the acid decomposable group can be increased by using a specific photoacid generator in which the acid strength has been increased.
However, not only in the formation of a minute pattern for increasing the degree of integration of an integrated circuit chip, in the formation of a minute pattern, it is important to uniformly miniaturize a resist pattern. In this regard, critical dimension (CD) refers to the dimension (width of an interconnect line, contact, trench or the like) of the smallest geometrical feature in the formation of a semiconductor device. For forming a uniform resist pattern, it is required to effectively control the deviation of CD.
Further, a resist composition is required to have improved exposure latitude (EL), so that a clear pattern can be formed even when there is shortage or excess of exposure in the formation of a resist pattern.